In recent years, from the viewpoint of reduction of fuel consumption and environmental protection, among work machines such as an excavator, there has been electric drive-type work machine driven by electricity. In such an electric drive-type work machine, electricity supplied to a power source includes an internal power supply type in which a battery is mounted on the work machine to receive electricity from the battery, and an external power supply type that receives electricity from the outside of the work machine by a cable. For example, a mobile equipment cable processing device described in Patent Literature 1 has a towing vehicle connected to the power supply by a cable, and the mobile equipment is connected to the power supply via the towing vehicle, further by being connected to the towing vehicle by the cable. Furthermore, in an electric drive-type construction machine described in Patent Literature 2, an electric motor mounted on an excavator is connected to a power supply by the cable, via an electric power standardization device mounted on a movable truck.
Furthermore, in a power supply system of an electric drive-type work machine described in Patent Literature 3, a power generator is mounted on a dump truck, and an excavator including a hydraulic pump driven by an AC motor connects the AC motor of the excavator and the power generator of the dump truck by a cable, or connects the AC motor of the excavator and the power generator via a transformer mounted on a movable truck. In this way, in the case in which an electric work machine such as an excavator is driven by an external power supply, it is possible to widen the range of movement of the work machine itself, by connecting the work machine and the power supply by a cable via the movable truck.